1. Field of the Invention
The present invention is applied to a gas engine provided with a spark plug, and relates to the gas engine provided with bore-cooling holes for cooling a circumferential space around the spark plug by use of a plurality of the bore-cooling holes.
2. Background of the Invention
FIG. 3 shows a cross-section around a pre-combust ion chamber 4 of a conventional gas engine provided with a spark plug, the cross-section including the vertical center axis of the pre-combustion chamber.
In FIG. 3, a pre-combustion chamber forming-piece (a pre-combustion chamber mouthpiece) 2 is fastened to and on the bottom wall of a cylinder head 1, the pre-combustion chamber forming-piece being surrounded by a water chamber 1a; and, the pre-combustion chamber 4 is formed inside the pre-combustion chamber forming piece.
A mounting hardware piece 13 for mounting the spark plug 13 thrusts the pre-combustion chamber forming-piece 2 toward the bottom wall of the cylinder head 1; thus, the pre-combustion chamber forming-piece 2 is fixed in the cylinder head.
The spark plug 10 (which vertical center axis is shown with the line 10a in FIG. 3) is fitted on the mounting hardware piece 13 via a fitting seat surface 50 and a gasket 10f, the spark plug being thrust toward the fitting seat surface and the gasket.
Into the pre-combustion chamber, a fuel gas (for the precombustion in the pre-combust ion chamber) is Supplied through a fuel inlet passage 14f a solenoid controlled valve (not shown in FIG. 3) that is arranged at the upstream side of the fuel inlet passage 14, and a check valve 51 that is a unidirectional valve which automatically opens with forward flow and closes against reverse flow. While the check valve is being opened, the fuel gas streams into the pre-combustion chamber 4 (which vertical center axis is shown with the line 4a in FIG. 3) through a fuel gas inlet slot 5; the fuel gas having streamed into the chamber 4 is ignited by the spark discharge at the spark plug; thus, flames and combustion gas is generated in the pre-combust ion chamber 4.
Further, the flames and combustion gas generated in the pre-combustion chamber 4 gush into the main combustion chamber 60 through at least one torch jet nozzle 3 provided at the lower part of the pre-combustion chamber forming piece; the flames and combustion gas gushing into the main combustion chamber 60 ignite the lean, prefixed air-fuel mixture that is induced into the main chamber 60 through the intake air passages (not shown); and, the lean, prefixed air-fuel mixture burns in the main chamber 4.
A cooling water streaming space 55 surrounds a mounting hardware piece 13 for mounting the spark plug 10; during the operation of the gas engine, circulating cooling water streams through the cooling water streaming space 55; thus, the outer circumference of the mounting hardware piece 13 and the inside thereof are cooled so as to restrain the temperature, rise as to the sparkplug 10.
On the other hand, in parallel with the development trend for higher output and higher efficiency in the field of gas engines, in the gas engine with the configuration as described above, the temperature of the spark plug 10, the temperature in the neighborhood of the fitting seat (part) of the spark plug 10 and the temperature of the check valve 51 prone to rise. Thus, it becomes necessary to take counter measures to restrain the temperature rise regarding the spark plug 10 and the components surrounding the plug 10.
The patent reference 1 (JP7-25224 [a utility model application]) discloses a configuration in which the fuel gas is supplied to the pre-combustion chamber 1 (in the figure of the reference 1); the fuel gas supplied to the pre-combustion chamber 4 is ignited by the spark discharge at the spark plug; thus, flames and combustion gas is generated in the pre-combustion chamber 4; the flames and combustion gas generated in the pre-combustion chamber 4 gushes into the main combustion chamber so that the lean, premixed air-fuel mixture that is induced into the main chamber is ignited, and burns. In addition, around the fitting (seat) part for fitting the spark plug, a plurality of bore-cooling holes (not-penetrating holes) is arranged; and, the inside of the bore-cooling holes is cooled by streaming water. Thus, the neighborhood, of the spark plug is cooled.
Further, according to the patent reference 2 (JP2007-100642), a volume part of a hollow shape is provided inside the circumferential wall of the pre-combustion chamber 4; in the volume part, a heat-transfer medium is filled so that the components around the spark plug are cooled by the heat exchange between the heat-transfer medium and the combustion gas produced inside the pre-combustion chamber; thus, the temperatures of the components around, the spark plug are controlled.
As described above, in the gas engine provided with the spark plug, the spark plug, the neighborhood of the seat surface of the fitting part for the spark plug and the check valve are heated up to a considerably high temperature. Therefore, it becomes necessary to take counter measures to restrain the temperature rise regarding the spark plug 10 and the components surrounding the plug 10.
In parallel with the development trend for higher output and higher efficiency in the field of gas engines, the gas engine provided with the spark plug as shown in FIG. 3 has to cope with the temperature rise, as the temperature rise causes the shortened life of the spark plug 10; more concretely, with the temperature rise, the temperature of the electrode section (i.e. center electrode and earth electrode) also becomes high, and the wear of the electrode section is quickened. Further, when the temperature level of the electrode section exceeds an allowable maximum threshold, abnormal combustion is caused in addition to the wear of the electrode section; namely, the excessive temperature causes the spontaneous combustion of the fuel gas around the electrode section at unexpected time points.
Further, the gas engine comprising the spark plug is provided with the check valve 51 directly above the pre-combustion chamber 4; the pressure of the gas in the pre-combustion chamber 4 works on the check valve 51, under a high temperature condition, while the fuel gas in the pre-combustion chamber 4 is often difficult to burn completely; the imperfect combustion causes soot, and the soot generated in the pre-combustion chamber 4 tends to be collected around the check valve 51. The soot deposit often causes the adhesion of the check valve toward the fitting component thereof; and, the soot deposit often causes the poor condition of the seat surface between the check valve and the bearing component thereof. Therefore, it becomes necessary to further reduce the temperature of the check valve and the surrounding component.
Hereby, attention is again paid to the patent reference 1 (JP7-25224 [a utility model application]), which discloses a cooling system (structure) for cooling the components in the neighborhood of the spark plug 10 by streaming cooling water in the bore-cooling holes that are provided along the circumference of the fitting part for fitting the spark plug 10.
However, the structure disclosed by the patent reference 2 is limited within a system in which the bore-cooling holes are provided simply at the circumference of the fitting part of the spark plug 10, and the neighborhood of the fitting part of the spark plug 10 is just cooled; namely, the patent reference 2 does not discloses a cooling means for cooling the whole part including the spark plug 10 and the check valve 51 by use of the bore-cooling approach; in addition, the patent reference 2 does not discloses an improving means for improving the cooling effect of the cooling structure on the fuel inlet connecting piece that has an inner passage through which the fuel gas is supplied to the pre-combustion chamber.